Sensitive optical instruments are often used in turbulent and dynamic environments. It is critical in these applications that the instrument remain at a user-established attitude in situations where the attitude of the platform to which the instrument is mounted is constantly changing. Applications such as filming underwater scenes where the camera is mounted on a submersible vehicle which roams the ocean floor is a typical scenario which highlights the need for a stable optical platform. Similarly, optical data links between ships require stable instrument platforms to maintain the transmission and reception equipment at a constant attitude despite the rolling and pitching of the ocean. Other instruments, such as laser range finders and laser targetting systems also require stable platforms to properly operate.
The prior art is replete with stabilized platforms that are mechanically gimbaled, thereby allowing the centrally positioned instrument (such as a compass) to remain at a desired attitude despite tilting or rotation of the surrounding structure that supports it. The mechanical gimbal allows the instrument mounted therein to maintain a constant attitude relative to an external frame of reference by means of mechanical or electromechanical linkages.
Referring to the prior art, U.S. Pat. No. 3,592,429 shown in FIG. 1 discloses a mechanically gimbaled platform for instruments. The device comprises a U-shaped base 1 mounted on a support 2 and a U-shaped cradle 3 swingably mounted on the base 1. The base comprises two interconnected units 4, 5 disposed one above the other and each including pistons rotatably mounted in liquid filled cylinders 6 (only the set in the uppermost portion is shown). The lowermost of the two units 5 is coupled to a support 2 such as a tripod (only two legs of which are shown), with the uppermost unit 4 secured to the underface of the base bottom. The mechanical linkages integral to this device isolate an instrument mounted in the U-shaped cradle 3 from any roll, pitch, or yaw movements imparted on the platform. The platform is thus essentially, but not completely, stable and free from outside turbulence. However, such a mechanically gimbaled platform typically requires many component parts with tight mechanical tolerances. This results in high manufacturing costs and a lowered time between failures. Also, should the instrument mounted in the U-shaped cradle 3 become misaligned, it cannot be corrected as there is no alignment means incorporated into the device.
Platforms for optical instruments are well known in the prior art, an example of which is described in U.S. Pat. No. 4,860,038 which is illustrated in FIG. 2. This underwater bubble camera comprises a substantially spherical housing 7 which is impermeable to water and includes a viewing port 8, a support member 9 interconnecting the spherical housing to a vehicular base, a camera 10 mounted in the spherical housing, and electromechanical means 11 connected to a cockpit (not shown) to facilitate movement of the camera by a user positioned in the cockpit. While this invention is very useful, human intervention is required to maintain the camera at a constant attitude when the vehicular base is rotated due to external forces acting on the vehicle.
In an attempt to overcome some of the problems inherent in mechanically gimbaled instruments platforms, floated gimbal platforms were developed as disclosed in U.S. Pat. No. 4,258,578 which is illustrated in FIG. 3. This device is designed for high "g" environments and serves to reduce or eliminate bending forces present in mechanically gimbaled systems, by floating the instrument platform 12 in a hollow sphere 13 such that the platform is neutrally buoyant in the flotation fluid. By eliminating bending forces, this device reduces measurement errors associated with the inertial instruments mounted on the instrument platform. Although the device is effective in eliminating bending forces, the structure by which this is accomplished is unduly complex. Further, the device is not optimized for mounting optical devices. Finally, the device does not include means for re-positioning the internally floated platform should it adopt an undesirable attitude.